Oh boy. When StarCraft came out in 1998, I got carried away with what seemed like limitless possibilities of the Campaign Editor, having previously toyed around with the map editor for Warcraft II. I was twelve. I started working on my own campaign as soon as I finished the game, and intended to make a full three-side story with a whopping fourteen missions per side, using every type of terrain for two missions per side. I even bought a mic for the PC to do some campaign voice-overs, inspired by the Antioch Chronicles. (nevermind that English is not my first language, and I was doing it entirely in English -- which was good language practice anyway).
Eventually the project was fleshed out into a twelve mission Terran campaign that was taking place after the vanilla ending, but completely discarding the events in the Brood War expansion. Sometime in 2003, I even got it included on a magazine coverdisk of a local (that is, Russian) gaming mag, complete with a small mod that optionally replaced one unit and added some custom weaponry to a few others -- I learned a bit of StarCraft modding too. I am honestly at a loss as of how to assess that campaign now. Making missions sure was more fun than playing them (save for playtesing), and back then I got to know the Campaign Editor and its many idiosyncrasies very well. The writing and plot are below average I guess, map design a mixed bag, and finally I think I went over the top with giving the player enough time to build up their bases in each mission, making the result not very challenging (I guess).
When Wacraft III came out I tried making a campaign for that one as well, but creating a full 3D terrain was a chore, and I did not like the world of Warcraft III as much as that of StarCraft anyway. I did make one and a half missions though before ditching the entire project.
Sometime later, in mid-2005 or so, I gave a go at making maps for the original Command & Conquer using the XCC Map Editor. I produced two maps which I think are decent and should be available somewhere for download, and the third one (which I actually started first) had some interesting ideas (I used the red multiplayer player to simulate a conflict within the Brotherhood) was left unfinished.
I never tried making any maps for a 2.5D or 3D FPS game though.